On Wed, Jun 23 2010 at 3:40pm -0400,
Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 23 Jun 2010 11:24:51 +0800
> Tao Ma <tao.ma@xxxxxxxxxx> wrote:
>
> > In submit_bio, we count vm events by check READ/WRITE.
> > But actually DISCARD_NOBARRIER also has the WRITE flag set.
> > It looks as if in blkdev_issue_discard, we also add a
> > page as the payload and the bio_has_data check isn't enough.
> > So add another check for discard bio.
> >
> > Cc: Jens Axboe <axboe@xxxxxxxxx>
> > Signed-off-by: Tao Ma <tao.ma@xxxxxxxxxx>
> > ---
> > block/blk-core.c | 2 +-
> > 1 files changed, 1 insertions(+), 1 deletions(-)
> >
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index f84cce4..a725602 100644
> > --- a/block/blk-core.c
> > +++ b/block/blk-core.c
> > @@ -1586,7 +1586,7 @@ void submit_bio(int rw, struct bio *bio)
> > * If it's a regular read/write or a barrier with data attached,
> > * go through the normal accounting stuff before submission.
> > */
> > - if (bio_has_data(bio)) {
> > + if (bio_has_data(bio) && !(rw & BIO_RW_DISCARD)) {
> > if (rw & WRITE) {
> > count_vm_events(PGPGOUT, count);
> > } else {
>
> Yes, that's a buglet.
>
> Note that Christoph's "[PATCH, RFC] block: don't allocate a payload for
> discard request" will fix it in a better way.
Oddly, even with Christoph's patch, bio_has_data() is still true once
the discard bio gets to DM.
Figuring out why is on my near-term TODO.
Mike
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